RNA Concentration Calculator
Calculate RNA concentration from A260 absorbance. Uses coefficient 40 ug/mL per OD260 for ssRNA. Assess purity by A260/A280 and A260/A230 ratios. Essential for RNA-seq and RT-PCR.
🧬 Molecular Biology📐 c = A260 x 40 x dilution🧬 Biology
Absorbance at 260nm (A260)
Dilution factor
A280 (for purity ratio)
A230 (optional)
Please enter valid values.
Formula & Reference
| Variable | Symbol | Formula | Units |
|---|---|---|---|
| RNA Concentration Calculator | — | c = A260 x 40 x dilution | ng/uL |
Step-by-Step Examples
Example 1
Total RNA Extraction
A260=0.38, no dilution.
- c = 0.38 x 40 = 15.2 ng/uL
- Total from 50uL eluate = 760 ng
- Suitable for RT-qPCR (typically need 50-500 ng)
✓ 15.2 ng/uL total RNA
Example 2
High-Yield Extraction
A260=1.85, no dilution.
- c = 1.85 x 40 = 74 ng/uL
- Check A260/A280 for purity
- If A280=0.93: ratio=1.99 — pure RNA
- Total from 30uL: 74 x 30 = 2220 ng
✓ 74 ng/uL, 2.2 ug total RNA
Example 3
Contaminated Sample
A260=0.50, A280=0.40.
- c = 0.50 x 40 = 20 ng/uL
- A260/A280 = 0.50/0.40 = 1.25
- Ratio < 1.8: heavy protein contamination
- Re-purify before RT-PCR or RNA-seq
✓ Contaminated RNA, re-purify needed
Real-World Applications
RNA-Seq
Accurate RNA quantification required for library input and normalization.
RT-PCR/qPCR
Input RNA quantity affects first-strand cDNA synthesis efficiency.
Diagnostic RNA Tests
COVID-19 PCR and other RNA virus diagnostics require quality RNA extraction.
Gene Expression Studies
Consistent RNA input amounts ensure reliable comparison across samples.
Common Mistakes to Avoid
⚠️
Using dsDNA coefficient (50) for RNA
RNA uses 40 ug/mL per OD (ssRNA), not 50 (dsDNA). Incorrectly using 50 overestimates RNA concentration by 25%.
⚠️
Not checking RNA integrity
A260 quantifies RNA but not its integrity. Degraded RNA gives same A260 as intact RNA. Run on gel or Bioanalyzer to check RIN (RNA Integrity Number).
⚠️
Forgetting DNase treatment
Genomic DNA contamination absorbs at 260nm, inflating apparent RNA concentration. Treat with DNase I before quantification for best accuracy.
Frequently Asked Questions
What is a good RNA yield? ▾
Depends on sample: total RNA from cell culture: 1-50 ug from 10^6 cells. FFPE tissue: 10-100 ng. Blood: 1-10 ug from 1mL. RNA-seq typically needs 100 ng - 1 ug.
What is RIN (RNA Integrity Number)? ▾
Score from 1-10 for RNA quality (Bioanalyzer). RIN 10 = fully intact. RIN > 7 for RNA-seq; RIN > 5 for qPCR. RIN < 5: highly degraded, unreliable for expression studies.
What is the difference between total RNA and mRNA? ▾
Total RNA: mix of rRNA (~80%), tRNA (~15%), mRNA (~3%), others. mRNA is poly-A selected or rRNA-depleted. RNA-seq libraries use either total RNA (with rRNA depletion) or poly-A selected mRNA.
What is the A260/A280 for pure RNA? ▾
2.0-2.2 for pure RNA. Below 2.0 suggests protein or DNA contamination. If 1.8-2.0 for RNA, the sample contains dsDNA. Use Dnase treatment and re-check.
Can I use TRIzol RNA for RT-PCR immediately? ▾
Yes, if residual ethanol is removed and RNA is dissolved in RNase-free water. Check A260/A230 for trace phenol/GITC contamination, which inhibits RT reaction.